The present invention relates generally to a wire sensing and measurement apparatus, and more particularly to such an apparatus for use in a wire pull machine for pull testing of electrical circuit wires.
Wire pull testing machines are used to determine the bond strength of leads which are attached to circuits. Machines of this type are described, for example, in U.S. Pat. Nos. 4,453,414 of Ronemus et al., 3,564,911 of Slemmons et al., and 3,572,108 of McShane et al. Generally, these machines comprise a wire hook member for hooking under a lead which is then moved away from the lead to apply a pulling force to the lead to test its strength. In some machines of this type a predetermined force is applied to the lead to test whether or not it will break or separate from the circuit under such loads. In other machines the wire is destructively tested by pulling until the wire or bond fails, and the force required is measured and used to adjust the wire bonding equipment, if necessary.
One problem with these wire pull testing machines is that they are commonly positioned by eye. This can be a problem in very small scale, microelectronic circuits involving many wire leads, since there is a good chance that the operator may miss one or more of the leads. Some automatic wire pull machines have been proposed which are programmed with all the wire positions and automatically position the pull hook beneath each stored wire position. However, these machines are also not sufficiently accurate since the position of all the wires in the circuit need not necessarily correspond precisely with the expected, stored wire position, for example if they have been displaced for some reason. In this case the machine will miss some of the wires altogether, as it is only capable of moving the hook sequentially to the stored wire positions. This results in an incomplete, and therefore unsatisfactory, test.